P0451

DTC P0451 EVAPORATIVE EMISSION CONTROL SYSTEM PRESSURE SENSOR PERFORMANCE





WIRING DIAGRAM

CIRCUIT DESCRIPTION
An evaporative emission control system is used to prevent emission of fuel vapor. The vapor generated in the fuel tank while driving or the engine at a stop passes through a tank pressure control valve and enters the EVAP canister where the charcoal absorbs and stores the fuel vapor. The EVAP canister purge valve is controlled as follows by ECM according to signals from various sensors.
- When the engine is normal operating temperature and the A/F is being fed back, ECM controls ON/OFF (open/close) switching of EVAP canister purge valve at a constant rate of 10 times/sec. and the length of its ON time depending on following factors so as to prevent the A/F from being changed suddenly.
- Engine speed
- Manifold absolute pressure
- Concentration of fuel vapor in purge line (fuel vapor concentration is calculated based on how much the feed back A/F changes when the canister is purged and not purged.)
When the EVAP canister purge valve opens, fuel vapor in the EVAP canister is sucked into intake manifold. At this time, EVAP canister is purged or cleaned by the air drawn through the air pipe. The tank pressure control valve is provided to keep the pressure in the fuel tank constant. When the pressure in the fuel tank becomes positive and reaches its specified value, it opens the valve to let the vapor flow into the EVAP canister. On the other hand, when the pressure in the fuel tank becomes negative and reaches its specified value, it opens the valve to let the air flow into the fuel tank.





DETECTING CONDITION

DTC CONFIRMATION PROCEDURE

WARNING:
- When performing a road test, select a place where there is no traffic or possibility of a traffic accident and be very careful during testing to avoid occurrence of an accident.
- Road test should be carried out with 2 persons, a driver and a tester, on a level road.

1) Turn ignition switch OFF.
2) Clear DTC with ignition switch ON.
3) Check vehicle and environmental condition for:
- Indication of fuel level meter in combination meter: within 1/4-3/4
- Altitude (barometric pressure): 2400m, 8000ft or less (560mmHg, 75kPa or more)
- Ambient temp.: -10°C, 14°For higher
- Intake air temp.: 70°C, 158°For lower
- Engine coolant temp.: 70 - 110°C, 158 - 230°F
4) Drive vehicle under usual driving condition (described in DTC P0136) for 15 min.
5) keep vehicle speed at 30-40mph, 50-60km/h and hold throttle valve at that opening position for 3 min.
6) Stop vehicle (do not turn ignition switch OFF) and confirm that "EVAP system TEST COMPLETED" is displayed in "READINESS TESTS" mode on scan tool.
If "TEST NOT COMPLTD" is still being displayed, repeat above steps 3) to 5).
7) Run engine at idle for 2 min.
8) Check DTC in "DTC" mode and pending DTC in "ON BOARD TEST" or "PENDING DTC" mode.














INSPECTION

WARNING: This work must be performed in a well ventilated area and away from any open flames such as gas hot water.